1. Field of the Invention
This invention relates to a pneumatic tire, and more particularly to an agricultural pneumatic tire comprising a tread provided with many directional slant lugs extending from a central portion of the tread toward both ends of the tread in a direction inclined with respect to a circumferential direction of the tire and alternately arranged right and left with respect to an equatorial plane of the tire at given intervals in the circumferential direction of the tire.
2. Description of Related Art
There have hitherto been proposed and practiced many agricultural pneumatic tires each comprising a tread provided with many directional slant lugs extending from a central portion of the tread toward both ends of the tread in a direction inclined with respect to a circumferential direction of the tire and alternately arranged right and left with respect to an equatorial plane of the tire at given intervals in the circumferential direction of the tire in order to ensure running performances such as traction performance, running performance and the like when the tire is run on muddy road or soft road.
Throughout the specification, the term "directional slant lugs" means lugs obliquely extending with respect to the circumferential direction and forming so-called directional tread pattern designating a rotating direction (forward running direction) RD when the tire is mounted onto a vehicle that an obliquely extended portion of the lug located at a side near to the equatorial plane first contacts with ground and the lug portion located far from the equatorial plane contacts with ground later, and a front side of the lug first contacting with ground in the forward running direction of the tire is "stepping-in side of the lug" and a rear side of the lug later contacting with ground in the forward running direction of the tire is "kicking-out side of the lug".
In such an agricultural pneumatic tire, the traction performance and mud splashing property are required as an important performance when the tire is run on muddy road or soft road. In order to decrease mud clogging on the muddy road, it is effective to widen a circumferential interval between the lugs arranged in the tread, but as the interval between the lugs becomes wider, ride comfortability against vibrations when the tire is run on general road are undesirably degraded.
On the other hand, as a lug forming angle or an angle of the lug inclined with respect to a direction parallel to an axial direction of the tire becomes small, the traction component becomes large, but the fluidity of mud between the lugs becomes small and the mud clogging is liable to be caused.